OnSong has recently released OnSong Premium which is a subscription service for users looking for the most powerful OnSong experience. While many add-ons originally released as in-app purchases are now premium features, you can still access these features and the other features of OnSong that you've previously purchased. You can learn more about OnSong Premium and these details on the OnSong Premium FAQ page or in the OnSong Premium tutorial.
Restore Past Purchases
If you do not have access to features you need, you likely just need to restore your past purchases. To do this, go into the Utilities Menu in OnSong by tapping on the gear icon in the Menubar. Tap on the Account option and locate the Add-ons section. This will display add-ons previously available in OnSong. Tap on the Restore Past Purchases button at the bottom of the screen. This will request a list of previous purchases you've made for OnSong which will likely prompt you to sign in to your Apple ID. Once authenticated, OnSong will unlock the add-ons you've purchased previously.